(a) Technical Field
The present disclosure relates to a separator for a fuel cell. More particularly, it relates to a separator for a fuel cell, in which a water discharge hole such as a venturi tube or a water discharge means including a metal plate for condensing water is provided on a land of the separator being in contact with a gas diffusion layer (GDL) of a fuel cell so that water generated by a reaction is easily discharged from the GDL through the water discharge means.
(b) Background Art
Generally, a polymer electrolyte fuel cell has some advantages such as higher efficiency, greater current density and output density, and shorter starting time, as compared to other types of fuel cells. Further, since a polymer electrolyte fuel cell employs a solid electrolyte, it is also free from corrosion and does not need to regulate the electrolyte. As the polymer electrolyte fuel cell is an environment-friendly power source that exhausts pure water, it is of interest to the automotive industry.
The structure of an exemplary fuel cell stack will be described with reference to FIG. 1. A membrane electrode assembly (MEA) is positioned in the center of each unit cell of the fuel cell stack. Preferably, the MEA comprises a polymer electrolyte membrane 10, through which hydrogen ions (protons) are transported, and catalyst layers including a cathode (air electrode) 12 and an anode (fuel electrode) 14, which are coated on both sides of the electrolyte membrane 10 so that hydrogen reacts with oxygen.
Preferably, a gas diffusion layer (GDL) 16 and a gasket 18 are sequentially stacked on the outside of the electrolyte membrane 10, i.e., on the outside where the cathode 12 and the anode 14 are respectively positioned. A separator (also called a bipolar plate) 20 including a flow field, through which reactant gases are suitably supplied and water generated by a reaction is suitably discharged, is preferably positioned on the outside of the GDL 16. In certain exemplary embodiments, an end plate 30 for supporting and fixing the above-described elements is suitably connected to the outermost surface.
As an oxidation reaction of hydrogen takes place at the anode 14 of the fuel cell stack, hydrogen ions (protons) and electrons are produced. Accordingly, the thus produced hydrogen ions and electrons are suitably transmitted to the cathode 12 through the electrolyte membrane 10 and the separator 20, respectively. At the cathode 12, the hydrogen ions and electrons transmitted from the anode 14 react with oxygen in the air supplied to the cathode 12 to produce water by an electrochemical reaction. Preferably, the electrical energy generated from the flow of electrons is suitably supplied to a load that requires electrical energy through a current collector plate (not shown) of the end plate 30.
In certain embodiments, and as can be seen from FIG. 2 showing the unit cell of the fuel cell stack that generates electrical energy based on the above structure, the separator 20 comprises a plurality of lands 32, which is a flat portion directly bonded to the GDL 16, and a plurality of flow fields (or channels) 34 formed between the respective lands 32, through which hydrogen or air passes. Further, the separator 20 serves as a path through which water generated at the cathode 12 is removed and functions to transmit generated electricity to the outside.
Generally, most conventional separators comprise a plurality of lands and a plurality of flow fields having a suitably concave convex shape. As shown in FIG. 3, the flow field preferably includes a linear flow field 36 and a serpentine flow field 38 suitably modified from the linear flow field. The serpentine flow field 38 has an advantage in that hydrogen and air collide with the wall surface of the corresponding flow field to change the movement direction, which facilitates the diffusion of hydrogen and air into the GDL 16, thereby considerably improving electricity generation.
As shown in FIG. 4, a large amount of water generated by a reaction at the cathode 12 is discharged from the GDL 16 through the flow fields 34 of the separator 20; however, air is supplied from the flow fields 34 of the separator 20 and diffused into the GDL 16. Accordingly, the flow of discharged water collides with the flow of diffused air, and thus the water and air flow suitably interfere with each other.
As a result, the water discharge flow is obstructed by the air flow, and thus the water discharge efficiency is suitably deteriorated; further, the air flow is obstructed by the water discharge flow, and thus the efficiency that the air is diffused into the GDL is suitably deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.